Multicomponent refrigerant fluids for low and cryogenic temperatures

ABSTRACT

Multicomponent refrigerant fluids for generating refrigeration, especially over a wide temperature range including cryogenic temperatures, which are advantageous over conventional refrigerant fluids especially for certain applications, and which are non-toxic, non-flammable and low or non-ozone-depleting and preferably are maintained in variable load form through compression, cooling, expansion and warming steps in a refrigeration cycle.

This is a Continuation-in-Part of prior U.S. application(s) Ser. No.09/545,670, Filing Date: Apr. 7, 2000 now U.S. Pat. No. 6,426,019 andwhich in turn is a Division of application Ser. No. 09/222,809, FilingDate Dec. 30, 1998 now U.S. Pat. No. 5,076,372.

TECHNICAL FIELD

This invention relates generally to refrigeration and, moreparticularly, to the use of multiple component refrigerant fluids usefulfor generating refrigeration. The invention is particularly useful forproviding refrigeration down to cryogenic temperatures.

BACKGROUND ART

Refrigeration is conventionally generated by compressing and thenexpanding a refrigerant fluid within a refrigeration circuit. Well knownexamples of such conventional systems include refrigerators and airconditioners. Typically the refrigerant is a single component fluidwhich undergoes a phase change at a required temperature from a liquidto a gas thus making its latent heat of vaporization available forcooling purposes. The efficiency of the conventional system can beimproved by using a multiple component fluid as the refrigerant whichcan provide variable amounts of refrigeration over a requiredtemperature range. However, known multiple component fluid refrigerationcycles cannot effectively provide refrigeration over a large temperaturerange down to colder cryogenic temperatures. Moreover, most well knownrefrigerant fluids are toxic, flammable and/or ozone depleting.

Accordingly it is an object of this invention to provide multiplecomponent refrigerant fluids which are useful for providingrefrigeration down to cryogenic temperatures.

SUMMARY OF THE INVENTION

The above and other objects, which will become apparent to those skilledin the art upon a reading of this disclosure, are attained by thepresent invention, which is described in detail below.

As used herein the term “variable load refrigerant” means a mixture oftwo or more components in proportions such that the liquid phase ofthose components undergoes a continuous and increasing temperaturechange between the bubble point and the dew point of the mixture. Thebubble point of the mixture is the temperature, at a given pressure,wherein the mixture is all in the liquid phase but addition of heat willinitiate formation of a vapor phase in equilibrium with the liquidphase. The dew point of the mixture is the temperature, at a givenpressure, wherein the mixture is all in the vapor phase but extractionof heat will initiate formation of a liquid phase in equilibrium withthe vapor phase. Hence, the temperature region between the bubble pointand the dew point of the mixture is the region wherein both liquid andvapor phases coexist in equilibrium. In the practice of this inventionthe temperature differences between the bubble point and the dew pointfor the variable load refrigerant is at least 10° K, preferably at least20° K and most preferably at least 50° K.

As used herein the term “fluorocarbon” means one of the following:tetrafluoromethane (CF₄), perfluoroethane (C₂F₆), perfluoropropane(C₃F₈), perfluorobutane (C₄F₁₀), perfluoropentane (C₅F₁₂),perfluoroethene (C₂F₄), perfluoropropene (C₃F₆), perfluorobutene (C₄F₈),perfluoropentene (C₅F₁₀), perfluorohexane (C₆F₁₄),hexafluorocyclopropane (cyclo-C₃F₆) and octafluorocyclobutane(cyclo-C₄F₈).

As used herein the term “hydrofluorocarbon” means one of the following:fluoroform (CHF₃), pentafluoroethane (C₂HF₅), tetrafluoroethane(C₂H₂F₄), heptafluoropropane (C₃HF₇), hexafluoropropane (C₃H₂F₆),pentafluoropropane (C₃H₃ F₅), tetrafluoropropane (C₃H₄F₄),nonafluorobutane (C₄HF₉), octafluorobutane (C₄H₂F₈), undecafluoropentane(C₅HF₁₁), decafluoropentane (C₅H₂F₁₀), methyl fluoride (CH₃F),difluoromethane (CH₂F₂), ethyl fluoride (C₂H₅F), difluoroethane(C₂H₄F₂), trifluoroethane (C₂H₃F₃), difluoroethene (C₂H₂F₂),trifluoroethene (C₂HF₃), fluoroethene (C₂H₃F), pentafluoropropene(C₃HF₅), tetrafluoropropene (C₃H₂F₄) trifluoropropene (C₃H₃F₃),difluoropropene (C₃H₄F₂), heptafluorobutene (C₄HF₇), hexafluorobutene(C₄H₂F₆) and nonafluoropentene (C₅HF₉)

As used herein the term “hydrochlorofluorocarbon” means one of thefollowing: chlorodifluoromethane (CHClF₂), chlorofluoromethane (CH₂ClF),chloromethane (CH ₃Cl), dichlorofluoromethane (CHCl₂F),chlorotetrafluoroethane (C₂HClF₄), chlorotrifluoroethane (C₂H₂ClF₃),chlorodifluoroethane (C₂H₃ClF₂), chlorofluoroethane (C₂H₄ClF),chloroethane (C₂H₅Cl), dichlorotrifluoroethane (C₂HCl₂F₃),dichlorodifluoroethane (C₂H₂Cl₂F₂), dichlorofluoroethane (C₂H₃Cl₂F),dichloroethane (C₂H₄Cl₂), trichlorofluoroethane (C₂H₂Cl₃F),trichlorodifluoroethane (C₂HCl₃F₂), trichloroethane (C₂H₃Cl₃),tetrachlorofluoroethane (C₂HCl₄F), chloroethene (C₂H₃Cl), dichloroethene(C₂H₂Cl₂), dichlorofluoroethene (C₂H₂ClF), dichloropentafluoropropane(C₃HCl₂F₅) and dichlorodifluoroethene (C₂HClF₂).

As used herein the term “fluoroether” means one of the following:trifluoromethyoxy-perfluoromethane (CF₃—O—CF₃),difluoromethoxy-perfluoromethane (CHF₂—O—CF₃),fluoromethoxy-perfluoromethane (CH₂F—O—CF₃),difluoromethoxy-difluoromethane (CHF₂—O—CHF₂),difluoromethoxy-perfluoroethane (CHF₂—O—C₂F₅),difluoromethoxy-1,2,2,2-tetrafluoroethane (CHF₂—O—C₂HF₄),difluoromethoxy-1,1,2,2-tetra-fluoroethane (CHF₂—O—C₂HF₄),perfluoroethoxyfluoromethane (C₂F₅—O—CH₂F),perfluoromethoxy-1,1,2-trifluoroethane (CF₃—O—C₂H₂F₃),perfluoromethoxy-1,2,2-trifluoroethane (CF₃O—C₂H₂F₃),perfluoroethoxy-methane (C₂F₅—O—CH₃), perfluoropropoxy-methane(C₃F₇—O—CH₃), perfluorobutoxy-methane (C₄F₉—O—CH₃),cyclo-1,1,2,2-tetrafluoropropylether (cyclo-C₃H₂F₄—O—),cyclo-1,1,3,3-tetrafluoropropylether (cyclo-C₃H₂F₄—O—),perfluoromethoxy-1,1,2,2-tetrafluoroethane (CF₃—O—C₂HF₄),cyclo-1,1,2,3,3-pentafluoropropylether (cyclo-C₃H₅—O—),perfluoromethoxy-perfluoroacetone (CF₃—O—CF₂—O—CF₃),perfluoromethoxy-perfluoroethane (CF₃—O—C₂F₅),perfluoromethoxy-1,2,2,2-tetrafluoroethane (CF₃—O—C₂HF₄),perfluoromethoxy-2,2,2-trifluoroethane (CF₃—O—C₂H₂F₃),cyclo-perfluoromethoxy-perfluoroacetone (cyclo-CF₂—O—CF₂—O—CF₂—) andcyclo-perfluoropropylether (cyclo-C₃F₆—O).

As used herein the term “atmospheric gas” means one of the following:nitrogen (N₂), argon (Ar), krypton (Kr), xenon (Xe), neon (Ne), carbondioxide (CO₂), oxygen (O₂) and helium (He).

As used herein the term “hydrocarbon” means one of the following:hydrogen (H₂), methane (CH₄), ethane (C₂H₆), ethene (C₂H₄), propane(C₃H₈), propene (C₃H₆), butane (C₄H₁₀), butene (C₄H₈), cyclopropane(C₃H₆) and cyclobutane (C₄H₈).

As used herein the term “non-toxic” means not posing an acute or chronichazard when handled in accordance with acceptable exposure limits.

As used herein the term “non-flammable” means either having no flashpoint or a very high flash point of at least 600° K.

As used herein the term “low-ozone-depleting” means having an ozonedepleting potential less than 0.15 as defined by the Montreal Protocolconvention wherein dichlorofluoromethane (CCl₂F₂) has an ozone depletingpotential of 1.0.

As used herein the term “non-ozone-depleting” means having no componentwhich contains a chlorine, bromine or iodine atom.

As used herein the term “normal boiling point” means the boilingtemperature at 1 standard atmosphere pressure, i.e. 14.696 pounds persquare inch absolute.

As used herein the term “cryogenic temperature” means a temperature of150° K or less.

As used herein the term “indirect heat exchange” means the bringing oftwo fluids into heat exchange relation without any physical contact orintermixing of the fluids with each other.

As used herein the term “expansion” means to effect a reduction inpressure.

As used herein the terms “turboexpansion” and “turboexpander” meanrespectively method and apparatus for the flow of high pressure fluidthrough a turbine to reduce the pressure and the temperature of thefluid thereby generating refrigeration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generalized temperature versus concentration diagram for avariable load refrigerant mixture at a given pressure.

FIG. 2 is a schematic representation of a system wherein the inventionmay be practiced.

FIG. 3 is a schematic representation of another system wherein theinvention may be practiced.

FIG. 4 is a schematic representation of a three loop system wherein theinvention may be used to provide refrigeration over a wide temperaturerange.

DETAILED DESCRIPTION

The invention comprises a refrigerant mixture composed of definedcomponents in proportions which preferably form a variable loadrefrigerant mixture which may be used, for example, in a refrigerationcycle. The refrigerant mixture can be in all gas, gas/liquid, or allliquid phases depending on the process and the position within theprocess, i.e. the heat exchange position (top, middle, bottom).Preferably the cycle is a closed loop cycle. The refrigerant mixturesshow a smooth temperature change accompanying a phase change. This isdemonstrated in FIG. 1, a temperature versus concentration diagram of avariable load refrigerant mixture at a given pressure. With any givenmix of components A and B (xmix) at temperature (tmix), two phases willexist, the composition of the saturated vapor (xmixv) will differ fromthe liquid in equilibrium with the vapor and the liquid will have thecomposition (xmixl). As the temperature is lowered, both the liquidphase composition and the vapor phase composition will change, eachbecoming enriched in component B. The condensing mixture is constantlychanging its composition and thus its condensing temperature. It is thisfeature that makes it possible to improve the performance of arefrigeration cycle. The cycle improvement is related to the use ofmultiple components, each with its own normal boiling point andassociated latent heat of vaporization. The proper selection of therefrigerant components, optimum concentrations in the mixture, alongwith operating pressure levels, and refrigerant cycles, allows thegeneration of variable amounts of refrigeration over the requiredtemperature range. The provision of the variable refrigeration as afunction of the temperature allows the optimum control of heat exchangetemperature differences within the refrigeration user system and therebyreduces system energy requirements.

The variable load refrigerant mixture comprises at least one componentfrom the group consisting of fluorocarbons, hydrofluorocarbons andfluoroethers and at least one component from the group consisting offluorocarbons, hydrofluorocarbons, hydrochlorofluorocarbons,fluoroethers, atmospheric gases and hydrocarbons.

One preferred variable load refrigerant mixture comprises at least twocomponents from the group consisting of fluorocarbons,hydrofluorocarbons and fluoroethers and at least one component from thegroup consisting of fluorocarbons, hydrofluorocarbons,hydrochlorofluorocarbons, fluoroethers, atmospheric gases andhydrocarbons.

Another preferred variable load refrigerant mixture comprises at leastone fluorocarbon and at least one component from the group consisting ofhydrofluorocarbons and atmospheric gases.

Another preferred variable load refrigerant mixture comprises at leastone fluorocarbon, at least one hydrofluorocarbon and at least oneatmospheric gas.

Another preferred variable load refrigerant mixture comprises at leastthree components from the group consisting of fluorocarbons,hydrofluorocarbons and fluoroethers and at least one component from thegroup consisting of fluorocarbons, hydrofluorocarbons,hydrochlorofluorocarbons, fluoroethers, hydrocarbons and atmosphericgases.

Another preferred variable load refrigerant mixture comprises at leasttwo components from the group consisting of fluorocarbons,hydrofluorocarbons and fluoroethers and at least one atmospheric gas.

Another preferred variable load refrigerant mixture comprises at leasttwo components from the group consisting of fluorocarbons,hydrofluorocarbons and fluoroethers, at least one atmospheric gas and atleast one component from the group consisting of fluorocarbons,hydrofluorocarbons, hydrochlorofluorocarbons, fluoroethers, hydrocarbonsand atmospheric gases.

Another preferred variable load refrigerant mixture comprises at leasttwo components from the group consisting of fluorocarbons,hydrofluorocarbons and fluoroethers and at least two differentatmospheric gases.

Another preferred variable load refrigerant mixture includes at leastone fluoroether, i.e. comprises at least one fluoroether and at leastone component from the group consisting of fluorocarbons,hydrofluorocarbons, fluoroethers, hydrochlorofluorocarbons, hydrocarbonsand atmospheric gases.

In one preferred embodiment the refrigerant mixture contains nohydrochlorofluorocarbons. In another preferred embodiment therefrigerant mixture contains no hydrocarbons. Most preferably therefrigerant mixture contains neither hydrochlorofluorocarbons norhydrocarbons. Most preferably the variable load refrigerant isnon-toxic, non-flammable and non-ozone-depleting and every component ofthe refrigerant mixture is either a fluorocarbon, hydrofluorocarbon,fluoroether or atmospheric gas.

In one preferred embodiment the variable load refrigerant consistssolely of fluorocarbons. In another preferred embodiment the variableload refrigerant consists solely of fluorocarbons andhydrofluorocarbons. In another preferred embodiment the variable loadrefrigerant consists solely of fluorocarbons and atmospheric gases. Inanother preferred embodiment the variable load refrigerant consistssolely of fluorocarbons, hydrofluorocarbons and fluoroethers. In anotherpreferred embodiment the variable load refrigerant consists solely offluorocarbons, fluoroethers and atmospheric gases. Most preferably everycomponent of the variable load refrigerant is either a fluorocarbon,hydrofluorocarbon, fluoroether or atmosphere gas.

The invention is particularly advantageous for use in efficientlyreaching cryogenic temperatures from ambient temperatures. Tables 1-15list preferred examples of variable load refrigerant mixtures. Theconcentration ranges given in the Tables are in the mole percent. Theexamples shown in Tables 1-5 are preferred mixtures for generatingrefrigeration above about 200° K and the examples shown in Tables 6-15are preferred mixtures for generating refrigeration below about 200° K.

TABLE 1 COMPONENT CONCENTRATION RANGE C₅F₁₂ 5-35 C₄F₁₀ 0-25 C₃F₈ 10-50 C₂F₆ 10-60  CF₄ 0-25

TABLE 2 COMPONENT CONCENTRATION RANGE C₅F₁₂ 5-35 C₃H₃F₆ 0-25 C₃F₈ 10-50 CHF₃ 10-60  CF₄ 0-25

TABLE 3 COMPONENT CONCENTRATION RANGE C₃H₃F₅ 5-35 C₃H₃F₆ 0-25 C₂H₂F₄5-20 C₂HF₅ 5-20 C₂F₆ 10-60  CF₄ 0-25

TABLE 4 COMPONENT CONCENTRATION RANGE C₃F₄—O—CHF₃ 5-35 C₄F₁₀ 0-25CF₃—O—CHF₂ 10-25  CF₃—O—CF₃ 0-20 C₂F₆ 10-60  CF₄ 0-25

TABLE 5 COMPONENT CONCENTRATION RANGE C₃F₇—O—CH₃ 5-35 C₃H₂F₆ 0-25CF₃—O—CHF₂ 10-50  CHF₃ 10-60  CF₄ 0-25

TABLE 6 COMPONENT CONCENTRATION RANGE CF₅F₁₂ 5-25 C₄F₁₀ 0-15 C₃F₈ 10-40 C₂F₆ 0-30 CF₄ 10-50  Ar 0-40 N₂ 10-80 

TABLE 7 COMPONENT CONCENTRATION RANGE C₃H₃F₅ 5-25 C₄F₁₀ 0-15 C₃F₈ 10-40 CHF₃ 0-30 CF₄ 10-50  Ar 0-40 N₂ 10-80 

TABLE 8 COMPONENT CONCENTRATION RANGE C₃H₃F₅ 5-25 C₃H₃F₆ 0-15 C₂H₂F₄0-20 C₂HF₅ 5-20 C₂F₆ 0-30 CF₄ 10-50  Ar 0-40 N₂ 10-80 

TABLE 9 COMPONENT CONCENTRATION RANGE C₃F₇—O—CH₃ 5-25 C₄H₁₀ 0-15CF₃—O—CHF₂ 10-40  CF₃—O—CF₃ 0-20 C₂F₆ 0-30 CF₄ 10-50  Ar 0-40 N₂ 10-80 

TABLE 10 COMPONENT CONCENTRATION RANGE C₃H₃F₅ 5-25 C₃H₂F₆ 0-15CF₃—O—CHF₂ 10-40  CHF₃ 0-30 CF₄ 0-25 Ar 0-40 N₂ 10-80 

TABLE 11 COMPONENT CONCENTRATION RANGE C₅F₁₂ 5-25 C₄F₁₀ 0-15 C₃F₈ 10-40 C₂F₆ 0-30 CF₄ 10-50  Ar 0-40 N₂ 10-80  Ne 0-10 He 0-10

TABLE 12 COMPONENT CONCENTRATION RANGE C₃H₃F₅ 5-25 C₄F₁₀ 0-15 C₃F₈10-40  CHF₃ 0-30 CF₄ 10-50  Ar 0-40 N₂ 10-80  Ne 0-10 He 0-10

TABLE 13 COMPONENT CONCENTRATION RANGE C₃H₃F₅ 5-25 C₃H₂F₆ 0-15 C₂H₂F₄5-20 C₂HF₅ 5-20 C₂F₆ 0-30 CF₄ 10-50  Ar 0-40 N₂ 10-80  Ne 0-10 He 0-10

TABLE 14 COMPONENT CONCENTRATION RANGE C₃F₇—O—CH₃ 5-25 C₄F₁₀ 0-15CF₃—O—CHF₂ 10-40  CF₃—O—CF₃ 0-20 C₂F₆ 0-30 CF₄ 10-50  Ar 0-40 N₂ 10-80 Ne 0-10 He 0-10

TABLE 15 COMPONENT CONCENTRATION RANGE C₃H₃F₅ 5-25 C₃H₂F₆ 0-15CF₃—O—CHF₃ 10-40  CHF₃ 0-30 CF₄ 0-25 Ar 0-40 N₂ 10-80  Ne 0-10 He 0-10

One embodiment of the invention, which is particularly useful forgenerating refrigeration for use in a liquefier, is a multicomponentrefrigerant fluid comprising from 0.1 to 50 mole percent, preferablyfrom 16 to 31 mole percent, nitrogen, from 22 to 55 mole percent,preferably from 24 to 40 mole percent, tetrafluoromethane, and from 7 to48 mole percent, preferably from 11 to 23 mole percent,pentafluoroethane and/or perfluoropropane. By use of the term “and/or”it is meant that, in this instance, the third component, which ispresent in a concentration of from 7 to 48 percent, may be comprisedentirely of pentafluoroethane, or entirely of perfluoropropane, or maybe a mixture of pentafluoroethane and perfluoropropane. The term“and/or” is used in a similar manner for other formulations of theinvention which are listed below. A term which is equivalent to the term“and/or” as used herein is the term “at least one of”. This embodimentof the invention may also contain argon in a concentration up to 48 molepercent, perfluoropropoxy-methane in a concentration up to 30 molepercent, fluoroform in a concentration up to 25 mole percent,perfluorobutane in a concentration up to 20 mole percent, andperfluoropentane in a concentration up to 30 mole percent.

Another embodiment of the invention, which is particularly useful forgenerating refrigeration for use in a cryogenic air separation plant, isa multicomponent refrigerant fluid comprising from 0.1 to 45 molepercent argon, from 20 to 55 mole percent tetrafluoromethane, and from 7to 48 mole percent pentafluoroethane and/or perfluoropropane. Thisembodiment of the invention may also contain nitrogen in a concentrationup to 42 mole percent, perfluoropoxy-methane in a concentration up to 30mole percent, fluoroform in a concentration up to 25 mole percent,perfluorobutane in a concentration up to 15 mole percent, andperfluoropentane in a concentration up to 30 mole percent.

Another embodiment of the invention, which is particularly useful forgenerating refrigeration for use in such applications as forecooling andfood freezing, is a multicomponent refrigerant fluid comprising from 15to 85 mole percent tetrafluoromethane and from 15 to 85 mole percentpentafluoroethane and/or perfluoropropane. This embodiment of theinvention may also contain nitrogen in a concentration up to 25 molepercent, argon in a concentration up to 25 mole percent, krypton in aconcentration up to 25 mole percent, perfluoropropoxy-methane in aconcentration up to 30 mole percent, pentafluoropropane in aconcentration up to 30 mole percent, fluoroform in a concentration up to25 mole percent, perfluorobutane in a concentration up to 15 molepercent and perfluoropentane in a concentration up to 30 mole percent.

Another embodiment of the invention, which is particularly useful forgenerating low temperature though not cryogenic temperaturerefrigeration, such as at a temperature within the range of from 200K to260K, is a multicomponent refrigerant fluid comprising from 5 to 95 molepercent pentafluoroethane and/or perfluoropropane, and from 5 to 95 molepercent, perfluoropropoxy-methane and/or pentafluoropropane and/orhexafluoropropane. This embodiment of the invention may also containnitrogen in a concentration up to 10 mole percent, argon in aconcentration up to 10 mole percent, fluoroform in a concentration up to25 mole percent, tetrafluoromethane in a concentration up to 10 molepercent, and tetrafluoroethane in a concentration up to 20 mole percent.

Another embodiment of the invention, which is particularly useful forgenerating low temperature though not cryogenic temperaturerefrigeration, such as at a temperature within the range of from 200K to260K, is a multicomponent refrigerant fluid comprising from 20 to 65mole percent pentafluoroethane, from 20 to 65 mole percentdifluoromethane and from 7 to 55 mole percent pentafluoropropane. Thisembodiment of the invention may also contain nitrogen in a concentrationup to 10 mole percent, argon in a concentration up to 10 mole percent,fluoroform in a concentration up to 25 mole percent, tetrafluoromethanein a concentration up to 10 mole percent, and tetrafluoroethane in aconcentration up to 20 mole percent.

FIG. 2 illustrates one refrigeration cycle wherein the invention may bepracticed. Referring now to FIG. 2, the refrigerant mixture of thisinvention recirculates in a refrigeration circuit or loop 1. Refrigerant2 is compressed by passage through compressor 3 to form compressedrefrigerant fluid 4, cooled to near ambient temperature by passagethrough aftercooler 70, and then cooled and preferably at leastpartially liquefied by passage through heat exchanger 5. Unlessotherwise specified, each heat exchange step illustrated in the Drawingsis an indirect heat exchange step. Cooled refrigerant fluid 6 is thenthrottled, i.e. expanded, through valve 7 to a lower pressure. Thepressure expansion can be accomplished by a turbine, such as a gasexpansion, two-phase expansion, or liquid expansion turbine. Therefrigeration produced can be utilized at a single or narrow temperaturelevel by cooling a fluid 8 by indirect heat exchange in heat exchanger9, or can be utilized over a much wider temperature range in heatexchanger 5. The refrigeration may be used to cool one or more fluidstreams passing through heat exchanger 5 as illustrated bycountercurrent stream 10 and cocurrent stream 11. Although on an overallbasis, stream 11 is shown as being heated in exchanger 5, on a localbasis it can be cooled within exchanger 5. The resulting warmedrefrigerant mixture is then passed as stream 2 to compressor 3 and thecycle repeats.

The cooling arrangement could also include a precooler circuit or loop12 wherein a refrigerant mixture 13 of this invention designed toprovide refrigeration at intermediate temperature levels is compressedin precooler compressor 14, cooled to ambient temperature in aftercooler71, and the resulting compressed fluid 15 is cooled in heat exchanger 5.The resulting cooled fluid 16 is throttled through a valve or a suitableturbine 17 to generate refrigeration and resulting lower temperaturerefrigerant fluid 18 is warmed and then cycled as stream 13 tocompressor 14.

The effect of the precooler loop can be accomplished by intermediateremoval of some of the refrigerant mixture and recycling of liquid asillustrated in FIG. 3. The liquid recycle feature provides processflexibility in matching the refrigerant mixtures to the requiredtemperature ranges and avoids unnecessary cooling and potential freezingof the liquid refrigerant. The numerals in FIG. 3 are the same as thosein FIG. 2 for the common elements which will not be described again indetail. Referring now to FIG. 3, refrigerant fluid 20 is compressed bypassage through compressor 21 to form compressed refrigerant fluid 22which is cooled of the heat of compression to near ambient temperatureby aftercooler 71 and then cooled and partially condensed by partialtraverse of heat exchanger 5. Cooled two phase refrigerant mixture 23 ispassed into phase separator 24 wherein it is separated into vapor andliquid. Vapor 25 is further cooled through heat exchanger 5, throttledthrough valve 26 and warmed by passage through heat exchanger 9 and/or5. Liquid 27 is passed through valve 28 and then vaporized by passagethrough heat exchanger 5. In the embodiment illustrated in FIG. 3 theliquid is combined with the lower pressure vapor which is throttledthrough valve 26 prior to vaporization. The resulting warmed refrigerantmixture is then returned as stream 29 to compressor 21 and therefrigeration cycle begins anew. Although a single phase separation isillustrated, it is understood that multiple phase separations atdifferent temperature levels could be utilized to provide stagedprecooling circuits.

The invention is particularly useful for providing refrigeration fromambient temperature down to cryogenic temperature, even down to as low atemperature as 5° K. While the invention may be used to provide suchrefrigeration over this entire temperature range in a single loop, it isgenerally preferable to provide this refrigeration in a plurality ofcascade loops. The use of multiple cascade loops allows each circuit toprovide refrigeration over a selected temperature range. Thereby theselection of a suitable refrigerant mixture is facilitated, since theselected mixture need only be operable over a more limited temperaturerange. Note that although each cascade circuit is intended to providerefrigeration primarily over its associated temperature range, it mayalso provide some refrigeration at higher temperature levels. Thus thecascade circuits may somewhat overlap each other with respect toproviding refrigeration at a given temperature range.

The cascade loop system is illustrated in and discussed in conjunctionwith FIG. 4. Referring now to FIG. 4 higher temperature refrigerantfluid comprising two or more of, for example, tetrafluoromethane,fluoroform, perfluoropropane, perfluorobutane, pentafluoropropane,tetrafluoroethane, difluoromethoxy-difluoromethane and perfluoropentane,recirculates in higher temperature loop 30 wherein refrigeration isprovided from the ambient temperature of about 300° K down to about 200°K. The higher temperature refrigerant fluid 31 at about 300° K iscompressed in compressor 32, cooled through cooler 33 and heat exchanger60 and throttled through valve 34 to produce lower temperaturerefrigerant fluid 35 at about 200° K. The lower temperature refrigerantfluid is then warmed back to about 300° K and returned as stream 31 tocompressor 32.

Intermediate temperature refrigerant fluid, which may contain nitrogenand/or argon in addition to one or more of the components recited forthe higher temperature fluid, recirculates in intermediate temperatureloop 40 wherein refrigeration is provided from about 200° K down toabout 100° K. The intermediate temperature refrigerant fluid 41 iscompressed in compressor 42, cooled through cooler 43 and heatexchangers 60 and 61, and throttled through valve 44 to produce lowertemperature refrigerant fluid 45 at about 100° K which is warmed andthen returned as stream 41 to compressor 42.

Very low temperature refrigerant fluid comprising two or more ofnitrogen, argon, helium, neon and hydrogen recirculates in very lowtemperature loop 50 wherein the temperature level is brought from about100° K to about 20° K or even lower. The very low temperaturerefrigerant fluid 51 is compressed in compressor 52, cooled throughcooler 53 and heat exchangers 60, 61 and 62, and throttled through valve54 to produce lower temperature refrigerant fluid 55 at about 20° K orlower which is warmed by passage through warmer 56 and heat exchangers62, 61 and 60 and then returned as stream 51 to compressor 52.

The invention is especially useful for providing refrigeration over awide temperature range, particularly one which encompasses cryogenictemperatures. In a preferred embodiment of the invention each of thecomponents of the refrigerant mixture has a normal boiling point whichdiffers by at least 20 degrees Kelvin from the normal boiling point ofevery other component in that refrigerant mixture. This enhances theeffectiveness of providing refrigeration over a wide temperature range,particularly one which encompasses cryogenic temperatures. In aparticularly preferred embodiment of the invention, the normal boilingpoint of the highest boiling component of the multicomponent refrigerantfluid is at least 50° K, preferably at least 100° K, most preferably atleast 200° K, greater than the normal boiling point of the lowestboiling component of the multicomponent refrigerant fluid.

The components and their concentrations which make up the refrigerantmixture of this invention preferably are such as to form a variable loadrefrigerant mixture and preferably maintain such a variable loadcharacteristic throughout the whole temperature range of the method ofthe invention. This markedly enhances the efficiency with which therefrigeration can be generated and utilized over such a wide temperaturerange. The defined group of components has an added benefit in that theycan be used to form mixtures which are non-toxic, non-flammable and lowor non-ozone-depleting. This provides additional advantages overconventional refrigerants which typically are toxic, flammable and/orozone-depleting.

One preferred variable load refrigerant mixture which is non-toxic,non-flammable and non-ozone-depleting comprises two or more componentsfrom the group consisting of C₃F₇—O—CH₃, C₄H₅F₅, C₄H₄F₆, C₄F₄—O—CH₃,C₅H₂F₁₀, C₅HF₁₁, C₅F₁₂, CHF₂—O—C₂HF₄, C₄HF₉, C₃H₃F₅, C₂F₅—O—CH₂F,C₃H₂F₆, CHF₂—O—CHF₂, C₄F₁₀, CF₃—O—C₂H₂F₃, C₃HF₇, CH₂F—O—CF₃, C₂H₂F₄,CHF₂—O—CF₃, C₃F₈, C₂HF₅, CF₃—O—CF₃, C₂F₆, CHF₃, CF₄, O₂, Ar, N₂, Ne andHe.

The invention may be used to generate refrigeration for a large numberof uses, especially for cryogenic applications. Among such uses one canname gas separation processes such as cryogenic air separations andother cryogenic separations and natural gas upgrading, liquefiers, foodfreezing, vent gas recovery, heat pumping, cryogenic liquid storage andtransport vessel recondensation, crystallization, solidification, lowtemperature grinding, chemicals storage and transport, biological andmedical material storage and transport, and refrigerated rooms, i.e.cold rooms utilized for materials handling and storage.

Although the invention has been described in detail with reference tocertain preferred embodiments, those skilled in the art will recognizethat there are other embodiments of the invention within the spirit andthe scope of the claims.

1. A multicomponent refrigerant fluid comprising from 5 to 95 molepercent of at least one of pentafluorethane and perfluoropropane, andfrom 5 to 95 mole percent of at least one of perfluoropropoxymethane andpentafluoropropane and further comprising fluoroform in a concentrationup to 25 mole percent.
 2. A multicomponent refrigerant fluid comprisingfrom 5 to 95 mole percent of at least one of pentafluoroethane andperfluoropropane, and from 5 to 95 mole percent of at least one ofperfluoropropoxymethane and pentafluoropropane and further comprisingtetrafluoromethane in a concentration of from 10 to 50 mole percent. 3.A multicomponent refrigerant fluid comprising from 5 to 95 mole percentof at least one of pentafluoroethane and perfluoropropane, and from 5 to95 mole percent of at least one of perfluoropropoxymethane andpentafluoropropane and further comprising argon in a concentration up to40 mole percent.
 4. A multicomponent refrigerant fluid comprising from 5to 95 mole percent of at least one of pentafluoroethane andperfluoropropane, and from 5 to 95 mole percent of at least one ofperfluoropropoxymethane and pentafluoropropane and further comprisingnitrogen in a concentration of from 10 to 80 mole percent.
 5. Amulticomponent refrigerant fluid comprising from 5 to 95 mole percent ofat least one of pentafluoroethane and perfluoropropane, and from 5 to 95mole percent of at least one of perfluoropropoxymethane andpentafluoropropane and further comprising neon in a concentration up to10 mole percent.
 6. A multicomponent refrigerant fluid comprising from 5to 95 mole percent of at least one of pentafluoroethane andperfluoropropane, and from 5 to 95 mole percent of at least one ofperfluoropropoxymethane and pentafluoropropane and further comprisinghelium in a concentration up to 10 mole percent.